HDL cholesterol is one of the important items to be measured in medical examinations, various tests for clinical medicine, and the like, from the epidemiological viewpoint that the HDL cholesterol is correlated inversely with the frequency of the occurrence of coronary diseases. On the other hand, in clinical tests and the like, test pieces produced by impregnating filter paper or the like with a reagent and then drying it have been used widely because it is necessary to treat a large number of specimens.
One example of a method for measuring HDL cholesterol is separating HDL and other lipoproteins (such as LDL and VLDL) by ultracentrifugation, and then measuring only HDL cholesterol using an enzyme. Another example of the method is separating HDL and other lipoproteins by electrophoresis and staining the lipid to measure the intensity of the color developed. Although they are general methods for measuring HDL cholesterol, they are not practiced in the clinical tests or the like because they require a complicated operation, which makes it difficult to treat a large number of specimens. On this account, a variety of methods for measuring HDL cholesterol that enable the treatment of a large number of specimens have been proposed and are practiced actually in some clinical tests and the like. Examples of such methods will be described in the following.
For example, there have been proposed chemically modifying cholesterol esterase and cholesterol oxidase and specifically reacting the cholesterol in HDL in the presence of an inclusion compound such as cyclodextrin (JP 7(1995)-301636 A); adding an aggregating agent to a specimen to aggregate and settle lipoproteins other than HDL and then measuring HDL cholesterol present in the supernatant (for example, JP 8(1996)-131197 A, Japanese Patent No. 2600065, JP 8(1996)-201393 A, and Japanese Patent No. 2799835); and using a surfactant to generate a time period in which an enzyme reacts with HDL cholesterol specifically and measuring the HDL cholesterol in this time period (JP 11(1999)-56395 A). However, these methods are measurement methods applicable to a liquid system and cannot be applied directly to a test piece, which is a measurement method employing a dry system.
Examples of a method for measuring HDL cholesterol using a test piece include a method utilizing the above-described aggregation reaction (JP 2(1990)-210265 A, JP 3(1991)-99268 A, etc.). However, this method has a drawback in that it requires a filter separation mechanism or the like so that the structure of the test piece becomes complicated and a large amount of specimen is required.